An organic expander such as lignosulfonic acid or bisphenols condensate is added to a negative electrode material of the lead-acid battery. The organic expander prevents shrink of the negative electrode material, temporarily traps Pb2+ ions during charge-discharge, and further improves low-temperature high rate discharge performance.
With respect to the organic expander, Patent Document 1 (JP 3385879 B1) describes that when 90% or more of lignosulfonic acid is sulfonated, variations of the low temperature high rate discharge performance can be reduced. Patent Document 2 (JP-A-2013-41848) describes that when bisphenols condensate having an S element content of 6 to 10 mass % is used in place of the lignosulfonic acid, the charge acceptance performance is improved.
Aside from this, Patent Document 3 (JP-A-2003-142085) describes that when much graphite or carbon is added, a density of the negative active material is set to 2.5 to 3.8 g/cm3, and a battery is formed with an electrolyte solution containing at least one selected from among Sb, Sn, Bi, Zn, Se, Mn, Ca, Mg, and Sr, a lead-acid battery which bears up under high-temperature and has excellent high rate performance is obtained.